I haven't, at any time, doubted your ability to correctly configure an access point.

I'm just trying to find some data points that allow for an explanation of both "Eh, seems fine for me," and "Arrgh! This stuff doesn't work! Into the bin!"

I mean: I believe you when you say it doesn't work for you, for I have no reason not to believe you. And I assume that you also believe me when I say that it does work for me.

What other variables/data points could there be, do you suppose? It's hard, as you probably know, for me to imagine ways in which things can break when they've generally been working fine for me.

One possibly-related theoretical datapoint: My access points are not near eachother at all, on purpose. It is perhaps possible that the chatter from one of your APs was "desensing" (I hate that word, but it's a common-enough word) the front-end of the other AP and that this limits the ability of that AP to receive weak-ass signals from an ESP module (or whatever) in some manner of smart device. (When I do want to isolate wifi networks, like when my neighbor asks if he can borrow a cup of Internet because he's broke this month, I've been successful at creating virtual wireless interfaces that are steered to a particular VLAN -- even as far back as the WRT54G days.)

Another possibly-related data point: I do run my 2.4GHz channels at 20MHz bandwidth instead of 40MHz, because that always seemed to get better performance at a longer distance (not that I think I need that for most little in-home smart widgets, but it is nice to be able to take a wifi-connected speaker into the yard or out by the alley where I work on my car, and to use it without using bluetooth[0] or making my phone into a battery-sucking hotspot and reconfiguring the speaker to use that hotspot instead of the house's SSID).

In doing this, the best available throughput in my neighborhood is not very quick at 2.4GHz -- it's always down into low single-digit Mbps with 20MHz-wide 2.4GHz channels, which quite frankly sucks. But it always seems to work with a fairly consistent level of suck, and that level of suck is adequate (throughput-wise, at least) for what I actually need/want from 2.4GHz.

And, sure: I'd be happy to swing by with a few smart devices that seem to Just Work and one of my rather boring Mikrotik wAP ACs so we could sort it out. Or just share configs with passphrases and SSIDs sanitized? I don't think I'm doing anything special, but perhaps I am? (Perhaps I'm even doing something that is both wrong and stupid, but which lets it actually-work.)

I mean: At the end of the day, I just want other people to enjoy the same pleasure of being able to plug in random stuff and have it generally just behave. I don't think I'm an expert, though: I've got some background in land-mobile RF, have established some rather long links between Ethernet-connected devices using ISM bands (some of which have stood up for well over a decade), and I've been playing with Wifi since Orinoco PCMCIA cards were the new hotness. I think I know a few things, but that doesn't mean that I've got some super-secret sauce or something.

At home I'm just a cheap bastard who wants to automate some things, and who seems to be successful at getting inexpensive things like TP-Link smart plugs, ATHOM light bulbs, random Google/Amazon smart speakers, and trash-tier relay modules to work seemingly-reliably with Home Assistant over wifi. I'd pay more for Z-Wave or something if I felt that I had to do so, but my (perhaps unique) experience with wifi isn't leading me towards Z-Wave. (I also had good "luck" with X10 around a quarter of a century ago: It always worked well-enough to automate reliably as long as I kept everything X10-related far away, wiring-wise, from the beastly Best FerrUPS UPS I was using back then.)

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[0]: Most people would use Bluetooth for this, and they're generally not wrong. But I absolutely hate the way in which Bluetooth breaks when the person with a Bluetooth-connected speaker wanders off with their phone in their pocket and leaves their speaker behind: The audio breaks up in ways that are particularly annoying, but which they'll never, ever hear -- much to the disdain of anyone who does hear it happen. I don't like being that person. If I'm going to play music that the neighbors or anyone else can coincidentally hear, I don't want it to get broken and choppy just because I went inside the house to fetch a different wrench or a beer or something, even if I myself will never hear the problem that Bluetooth use can promote. In this way, slow wifi is better than broken Bluetooth.